Wide angle beam steerer using translation of plural lens arrays

ABSTRACT

A beam steering arrangement for a plurality of beams of electromagnetic radiation from a like plurality of sources arrayed with a preselected source-to-source spacing includes a first lens array. The period of the lenses corresponds to that of the sources. The lenses of the first array may be converging or diverging lenses, but when illuminated by the sources, each produces a beam of light including at least a diverging portion. A second lens array is cascaded with the first lens array, with the lenses of the second array illuminated by the diverging beam portions. The second lens array collimates the diverging beam portions. The second lens array is translated in a direction approximately transverse to the undeflected beam direction in order to scan or deflect the collimated beams. This may result in overfilling of the input apertures of the lenses of the output lens array, with consequent reduction in the amplitude of the main beam, and with generation of beams of lower intensity in other directions. The first lens array is translated in a fashion which scans the diverging beam portions to prevent aperture overfilling. In particular embodiments of the invention, the lenses of the output lens array are converging lenses, and the input lens array may include either converging or diverging lenses. In another embodiment of the invention, the pair of translatable lens arrays is cascaded with an array of phase shifters for providing piston phase correction by which a continuous range of scan directions may be achieved.

BACKGROUND OF THE INVENTION

This invention relates to the steering of beams of electromagneticradiation, such as light beams, by relative translation of lens arraysin combination with phase shifters.

Coherent beams of electromagnetic radiation are scanned for use incommunication systems, radar, weapons, welding, supermarket labelchecking, and optical disc reading and writing. Very often, thetransmitted beams are made up from a combination of plural individualbeams.

The scanning function may be provided by gimballed, mechanicallymoveable mirrors, lenses or reflectors. However, the mass of suchstructures may impede the ability to scan in a random fashion, althoughrepetitive scanning at high speeds may be possible. An article entitled"Binary micro optics: an application to beam steering", by Goltsos etal., published by Lincoln Laboratory in connection with the SPIE: OELASE 89, 1052 (January 89) describes the relative translation of a pairof microlens arrays for beam steering. As described in the article, beamsteering is accomplished by relative translation of a pair of microlensarrays cascaded in the path of an array of light beams. The translationof the microlens arrays is in a direction lateral to the beam direction,and the magnitude of the motion which is required for scanning is lessthan the diameter of the individual lens of the array.

FIG. 1a illustrates a portion of a cascade of two microlens arrays. InFIG. 1a, a scanner designated generally as 10 includes a first microlensarray 12 which includes individual lenses 14, 16, 18 and 20. Adjacentlight beams illustrated as 22, 24, 26 and 28 fill the apertures oflenses 14, 16, 18 and 20, respectively. Lenses 14-20 cause the lightbeams to converge toward focal points (not illustrated). A secondmicrolens array 32 includes diverging or defocussing lenses 34, 36, 38and 40. Microlens array 32 is capable of translation relative tomicrolens array 12 in a direction of arrows 41. When the lenses of themicrolens arrays 12 and 32 are registered, i.e., when the correspondinglenses are coaxial as illustrated in FIG. 1a, the output light beams,illustrated as 42, 44, 46 and 48, propagate parallel to the direction ofpropagation of incoming light beams 22, 24, 26 and 28, respectively.

FIG. 1b illustrates as plots 52, 54, 56 and 58 the phase of the wavefronts associated with light beams 42, 44, 46 and 48, respectively, as afunction of distance from an arbitrary reference point relative to thelens arrays. The spaces between plots 52, 54, 56 and 58 representregions in which the light beams have a small amplitude. In FIG. 1b,plots 52, 54, 56 and 58 are, in effect, portions or continuations of thesame straight dash-line 51 having the same phase. Other plots could bemade at other distances from the lens arrays, with the phases increasinggradually with increasing distance from the lens arrays, and with thephases recurring if reduced by subtraction of multiples of 2π.

As illustrated in FIG. 1a, the output apertures of the lenses of array32 are not filled. If the output apertures were filled, plots 52, 54, 56and 58 of FIG. 1b would run together to create a continuous phase frontrepresenting a coherent beam of light, the direction of propagation ofwhich is normal to the phase front.

FIG. 1c illustrates a portion of scanner 10 of FIG. 1a, with lenses 36and 38 of lens array 32 translated vertically upward (in the directionof arrow I) relative to corresponding lenses 16 and 18 of lens array 12,and with the input light beams 24 and 26 illustrated as not completelyfilling the input aperture to enable the beam paths to be clearlydepicted. As illustrated, output beams 44 and 46 propagate in adirection different from that of the incoming beams, i.e. the beams havebeen scanned. FIG. 1d illustrates the phase of the wave fronts of beams44 and 46. As illustrated in FIG. 1b, phase fronts 64 and 66 exhibit aslope, the normal to which defines the direction of propagation of thebeam. As also illustrated in FIG. 1d, there is an offset, which isillustrated between arrows 50, which represents the offset between thephases of adjacent continuations of beams 44 and 46 of FIG. 1c. If thisphase offset is zero or zero plus a multiple of 2π, the beams arein-phase for the illustrated direction of propagation, and a beammaximum occurs. In general, however, the phase offset will vary with thescanning direction, with the result that for some scanning directionsthe individual beams will be mutually out-of-phase with another beam,resulting in destructive interference. This in turn results in afar-field scanned radiation pattern which contains grating lobes orangles at which the radiated energy is high, and other angles at whichthe radiated energy is low. The result of translating a lens array inone direction is to gradually reduce the amplitude of one grating lobe,while the adjacent grating lobe becomes larger. The Goltsos et al.article suggests the use of a scanning mirror at the system input forfine or vernier beam steering. Such a scanning mirror has thedisadvantages of a mechanical system referred to above, and in addition,causes the beams to enter the lenses of the lens array at an angle,which reduces the efficiency of the lens. This may be particularlyimportant when two lens arrays are involved, because the entry at anangle occurs in both lens arrays, so the losses are cascaded. It isdesirable to scan in a manner which allows the beam(s) to be directed atany angle, and not just at angles at which grating lobes occur.

FIG. 2a illustrates a lens array similar to that of FIG. 1, with thelenses of the two arrays registered, and FIG. 2b illustrates the samearrangement with one of the arrays laterally offset by translation inthe direction of arrow I. In FIG. 2, elements corresponding to those ofFIG. 1 are designated by the same reference numerals. In FIG. 2a,circular input light beams 24 and 26 are centered on axes 6 and 8,respectively, and fill the apertures of converging lenses 16 and 18,pursuant to the Goltsos et al. suggestion. Lenses 16 and 18 focus thelight to form converging beam portions 74 and 76, respectively, whichcome to a focus at a focus plane 99. From focus plane 99, diverging beamportions 84 and 86 propagate toward the input apertures of converginglenses 234 and 236, respectively. As illustrated, the spacings are suchthat beam portions 84 and 86 do not fill the apertures of lenses 234 and236. Lenses 234 and 236 collimate the beams to produce parallel outputbeams 44 and 46, respectively, which are centered on axes 4 and 6,respectively.

FIG. 2b illustrates the result of moving lens array 32 of FIG. 1adownward, in the direction of arrow I. As illustrated, light beams 84and 86 intercept lenses 234 and 236 in a region in which the lenscurvature causes output beams 44 and 46 to be deflected or scanneddownward.

FIG. 3a is identical in subject matter to FIG. 1c, and is included as areference for comparison with FIG. 3b. In FIG. 3b, array 32, whichincludes diverging lenses 36 and 38, has been moved or translated upwardin the direction of arrow I, thereby causing exit beams 44 and 46 to bedeflected downward.

By comparison of FIGS. 2b and 3b, it is apparent that deflection ofoutput beams in a given direction in accordance with the Goltsos et al.arrangement requires that the output lens array be moved in thedirection of the desired deflection in the case of converging lensarray, and in a direction opposite to the desired scanning direction fora diverging lens array.

In FIG. 4, an arrangement similar to that of FIG. 2 has had its outputlens array 32 translated upward by an amount Δ in an attempt to increasethe scan angle. As illustrated, translation Δ is sufficient to causediverging light beam portion 84 to illuminate portions of both lenses234 and 236. This may be viewed as a form of overfilling of the apertureof lens 234. As illustrated, output beam 244 is deflected or scannedupward by lens 234. That portion of beam 84 falling onto lens 236,however, is deflected downward. When overfilling of the aperture occursin this manner, the far-field peak beam amplitude decreases, because theeffective aperture decreases. Put another way, translation of the movinglens array in the direction of the arrow in any of FIGS. 2, 3 or 4 mayresult in a secondary portion of each beam (246) being directed awayfrom the main scanned beam (244). The energy which goes into thesecondary beam is not available for the main beam, and the secondarybeam amounts to a scanning sidelobe which may not be desired. Theundesirable effect of overfilling also occurs with the arrangement ofFIG. 3. It would be advantageous to be able to translate the lenses toachieve additional scanning, with less loss of peak amplitude.

SUMMARY OF THE INVENTION

A beam steering arrangement for a plurality of beams of electromagneticradiation from a like plurality of sources arrayed with a preselectedsource-to-source spacing includes a first lens array. The period of thelenses corresponds to that of the sources. The lenses of the first arraymay be converging or diverging lenses, but when illuminated by thesources, each produces a beam of light including at least a divergingportion. A second lens array is cascaded with the first lens array, withthe lenses of the second array illuminated by the diverging beamportions. The second lens array collimates the diverging beam portions.The second lens array is translated in a direction approximatelytransverse to the undeflected beam direction in order to scan or deflectthe collimated beams. This may result in overfilling of the inputapertures of the lenses of the output lens array, with consequentreduction in the amplitude of the main beam, and with generation ofbeams of lower intensity in other directions. The first lens array istranslated in a fashion which scans the diverging beam portions toprevent aperture overfilling. In particular embodiments of theinvention, the lenses of the output lens array are converging lenses,and the input lens array may include either converging or diverginglenses. In another embodiment of the invention, the pair of translatablelens arrays is cascaded with an array of phase shifters for providingpiston phase correction by which a continuous range of scan directionsmay be achieved.

DESCRIPTION OF THE DRAWING

FIGS. 1a and 1c illustrate prior art microlens array pairs inuntranslated and relatively translated conditions, respectively, andFIGS. 1b and 1d represent the phase response of the output beams ofFIGS. 1a and 1c, respectively; FIGS. 1a, 1b, 1c and 1d are jointlyreferred to as FIG. 1;

FIGS. 2a and 2b, referred to jointly as FIG. 2, are simplifiedillustrations of prior-art pairs of converging lens arrays inuntranslated and translated conditions, respectively;

FIGS. 3a and 3b, referred to jointly as FIG. 3, are simplifiedillustrations of prior-art pairs of mixed converging and diverging lensarrays in untranslated and translated conditions, respectively;

FIG. 4 illustrates the effect of overfilling an aperture of thearrangement of FIG. 2 due to excessive translation;

FIG. 5a is an isometric or perspective view of a two-dimensional arrayof light sources such as an array of lasers cascaded with a microlensarray and a phase-shifter array in accordance with an aspect of theinvention,

FIGS. 5b and 5d are simplified side views of a portion of thearrangement of FIG. 5a, and

FIGS. 5c and 5e are plots of phase profile of the beams for thearrangements of FIGS. 5b and 5d; respectively,

FIGS. 5a, 5b, 5c, and 5d and 5e are jointly referred to as FIG. 5;

FIGS. 6a and 6b, referred to jointly as FIG. 6, illustrate thecombination of an array of sources and a pair of converging lens arrayswhich are translatable relative to the source array in accordance withan aspect of the invention;

FIGS. 7a and 7b, referred to jointly as FIG. 7, are similar to FIGS. 6aand 6b, respectively, but one of the lens arrays is a diverging lensarray;

FIGS. 8a, 8b and 8c illustrate a cascade of two converging lens arrays,one translatable and one not, with a phase shifter array located in thecascade before, between and behind the lens arrays, respectively, inaccordance with an aspect of the invention;

FIGS. 9a, 9b and 9c illustrate a cascade of a fixed diverging lens arraywith a translatable converging lens array, with a phase shifter arraylocated in the cascade before, between and behind the lens arrays,respectively, in accordance with an aspect of the invention;

FIGS. 10a, 10b and 10c illustrate a cascade of a pair of translatableconverging lens arrays, with a phase shifter array located in thecascade before, between and behind the lens arrays, respectively, inaccordance with an aspect of the invention,

FIGS. 11a, 11b and 11c illustrate a cascade of a translatable diverginglens array and a translatable converging lens array, with a phaseshifter array located in the cascade before, between and behind the lensarrays, respectively, in accordance with an aspect of the invention.

FIGS. 12a and 12b schematically illustrate a liquid crystal phase cellwhich may be used in the phase shifter array of FIG. 5, and themolecular reorientation which induces a phase change in lighttransversing the cell;

FIG. 13 schematically illustrates a liquid crystal prism phase cell forinducing a phase change which differs for light traversing variouslocations of the cell;

FIG. 14 illustrates an electromechanical phase shifter array usingelectromechanical actuators for reflective elements, and FIG. 15illustrates how they are used in a location before a cascade of two lensarrays;

FIG. 16 is a plot of beam irradiance versus scan angle for a prior artscanning arrangement such as that of FIG. 1 or 2;

FIG. 17 is a plot of beam irradiance versus scan angle for anarrangement according to the invention, such as the arrangement of FIGS.6 or 7, showing an amplitude advantage at large scan angles;

FIGS. 18a and 18b illustrates cascaded lens arrays in which the lensesare not arrayed in a regular or periodic fashion; and

FIG. 19 is a plan view of a cascade of sources, lenses, and phaseshifters, which are arrayed in a nonplanar fashion, but in which thearray elements subtend corresponding angular dimensions as seen from apoint.

DESCRIPTION OF THE INVENTION

In FIG. 5a, a rectangular array 522 of small or point sources ofelectromagnetic (EM) radiation includes array elements 524, 526, 528 and530. Radiation beams emitted from the sources of the array are centeredon axes, such as axes 508 and 509, and pass through microlenses of amicrolens array 510. For example, light from source 524 of source array522 passes through microlens 514 of array 510. The microlenses of array510 affect or modulate the phase distribution of the wavefronts of theelectromagnetic radiation passing therethrough, in a manner whichdepends upon the curvature of the lens. The phase modulated light thenpasses through a phase shifter of phase shifter array 540. For example,light leaving microlens array 514 in the general direction of axis 508passes in turn through phase shifter element or cell 544 of phaseshifter array 540. FIGS. 5b and 5d are simplified elevation views of thearrangement of FIG. 5a.

A control arrangement illustrated as a block 590 in FIG. 5a is coupled,mechanically or electrically, as may be required, to microlens array 510and to phase shifter array 540, for controlling the translation of thelenses of microlens array 510 and for controlling the phase shiftsimparted by the phase shifters of the phase shifter array 540. The phaseshifter array may be of the type described below, which is alsodescribed in the paper "Phase Control of Coherent Diode Laser ArraysUsing Liquid Crystals", by Cassarly and Finlan, published as paper No.18 in Volume 1043 in connection with the Proceedings of the SPIE: OELASE 89 convention, January 1989.

FIG. 5b illustrates in simplified side view the light paths associatedwith the arrangement of FIG. 5a when the light sources of source array522, the lenses of microlens array 510, and the phase shifters of phaseshifter array 540 are registered or aligned coaxially. As illustrated inFIG. 5b, light leaving source 524 diverges, and is converted byconverging lens 514 into a collimated beam, which passes through phaseshifter 544, centered on axis 508. The light from each of sources 526,528 and 530 similarly diverges from the source, is collimated by theassociated converging lens 516, 518 and 520, respectively, and passesthrough the associated phase shifter 546, 548 and 550. FIG. 5cillustrates as plots 552, 554, 556 and 558 the phases of the portions ofthe wavefront leaving the phase shifter array. Under the illustratedconditions, the phase shifters are arranged to produce no phase shiftrelative to each other. The phase front of the beam is constant acrossthe entire beam, resulting in a coherent combined beam extendingparallel to axes 508 and 509.

FIG. 5d is similar to FIG. 5a, and corresponding elements are designatedby the same reference numerals. In FIG. 5d, microlens array 510 istranslated upward relative to source array 522 and phase shifter array540. As illustrated, sources 524, 526, 528 and 530 are directional, andthe beam of light which each emits illuminates only one lens. FIG. 5eillustrates the phase of the beams. As illustrated in FIG. 5e, line 562represents the sloped phase of the beam leaving phase shifter 544.Similarly, plots 564, 566 and 568 represent the phase characteristics ofthe beams leaving phase shifters 546, 548 and 550, respectively. Inaccordance with an aspect of the invention, the phase shifters of phaseshifter array 540 are controlled so that the phase error betweenadjacent portions of the wavefront (the phase between arrows 560 in FIG.5e) is equal to zero or to an integer multiple of 2π. Thus, the phasedifference indicated as 560 in FIG. 2e, and all other such phase errors,are controlled by controller 590 of FIG. 5a to set the associated phaseshifter to equal 0 or 2Nπ. By reduction, this is equivalent to havingthe value of N equal to one. In effect, this creates a continuous phaseacross the entire combined beam, as suggested by plot 562 in combinationwith dashed line 570. The salient characteristic of the structure suchas that of FIG. 5a in combination with controlled phase shifters is thatbeam scanning can be accomplished over a wide angle with minimizedgrating lobes. Put another way, the scanning is continuous rather thandiscontinuous. In this context, the term "scanning" means the ability todirect the beam at any selected angle within a range of possible angles.

A further advantage of the arrangement according to the invention isthat, if the phase shifters of the phase array 540 are electricallycontrolled, the fine tune beam steering is nonmechanical. Additionaladvantages are that the use of multiple array elements tends to averageout construction and other errors in each element, thereby providinghigh pointing accuracy. This may be particularly important inapplications where the beam divergence is small. The translations of themicrolens array 510 which are necessary to provide scanning are smallerthan the lens diameters, and may be on the order of tens to hundreds ofmicrons. Thus, inertia effects are minimized. Also, the assembly may beof small size, light weight, and may scan with little power consumption,which is advantageous for many applications but particularly forspacecraft. Further, the phased array portion of the assembly can beused to increase beam divergence, which may be useful in acquisitionscenarios in which jitter at the transmitter site might cause the beamto miss the desired target.

Control 590 of FIG. 5a may use addressable memories (not separatelyillustrated) which are programmed with information relating to themechanical actuator position for lens array 510 and with the voltage foreach phase shifter, both as a function of angle. The information for thememories is initially established by adjusting the position of lensarray 510 and the voltages of the phase shifters to direct the beam orbeams at the desired angle. When the beam has been directed and adjustedat that angle, the lens position control information and the phaseshifter voltage information is written into memory locations whoseaddresses represent the desired angle. When information relating to allthe desired angles has been stored in memory, it is only necessary toread the memory or memories at the address(es) representing the desiredangle, and to use the information read from the memories to control thearrays. It should be noted that each memory address might include onlytwo items of information, namely the lens array actuator position and anelectrical device signal which is divided in a fixed ratio forapplication of a part thereof to each phase shifter of the array, or thememory could include information relating to an individually selectedvoltage for each phase shifter element, so as to provide for correctionof minor element-to-element phase discrepancies attributable toconstruction or other errors.

The sources of source array 522 of FIG. 5 have been described asdirectional, which will be the case if the sources are lasers, laserdiodes or a single light-emitting diodes (LEDs). The array of sourcescould alternatively be an array of pinholes, whereby the light from thesources would not be directional. In this event, the main beam producedat the output of phase shifter array 540 would be as described inconjunction with FIG. 5, but there would in addition be an array ofsidelobes of lesser amplitude, arising from the cross-illumination ofthe input apertures of the lenses of array 510 by nearby sources. Suchside lobes may be advantageous for some uses and disadvantageous forother uses.

FIGS. 6a and 6b, and FIGS. 7a and 7b, illustrate portions of scannersusing double-lens-array translation, and converging and/or diverginglenses. Each of the combinations can be cascaded with a piston phaseshifter according to the invention to achieve continuous scanning, asdescribed below. In accordance with an aspect of the invention, theinput apertures are unfilled.

FIG. 6 illustrates an arrangement similar to that of FIG. 2. Elements ofFIG. 6 corresponding to those of FIG. 2 are designated by the samereference numerals. As illustrated in FIG. 6a, sources 526 and 528 of asource array 522 produce light beams 24 and 26, respectively, which donot fill the input apertures of lenses 16 and 18, respectively, of lensarray 12. However, exit beams 44 and 46 fill the exit apertures oflenses 234 and 236 of the array. If translation of lenses 234 and 236were to be performed for scanning as in the prior art, withoutadditional translation according to the invention, even a small amountof scanning would cause the beams to overfill into the adjacent lens,thereby resulting in reduction of peak beam amplitude and production ofside lobes.

FIG. 6b illustrates translation of the lenses in accordance with theinvention. As illustrated in FIG. 6b, lenses 16 and 18 of input lensarray 12 are translated in the direction of arrow I, and lenses 234 and236 of output lens array 32 are translated by a greater amount in thedirection of arrow II. As illustrated, the directions of arrows I and IIare downward. The translation of lenses 16 and 18 deflects beam portions74, 76 and 84, 86 downward as illustrated in FIG. 6b, thereby causingthe beams entering output lenses 234 and 236 to continue to fill but notoverfill the apertures, and to thereby continue to associate each beamwith a corresponding one of the lenses of the array. In this manner,increased scanning can be achieved without amplitude reduction of thebeam due to overfilling of the apertures.

FIG. 7 is generally similar to FIG. 3, but with reversed positions inthe cascade of the converging and diverging lens arrays. Elements ofFIG. 7 corresponding to those of FIG. 3 are designated by the samereference numerals. In FIG. 7a, source array 522 produces beams 24 and26 as described in conjunction with FIG. 6. Beams 24 and 26 do not fillthe input apertures of lenses 36 and 38, but output beams 44 and 46completely fill the output apertures of lenses 16 and 18, respectively.In FIG. 7b, lenses 16 and 18 of lens array 12 are translated downward inthe direction of arrow II, thereby deflecting output beams 44 and 46downward. As discussed above, any translation of the output lens arraywhen the input and output apertures of the lenses of the output lensarray are full would result in a reduction of peak beam amplitude andgeneration of sidelobes if the translation were accomplished asdescribed in conjunction with FIG. 3. According to the invention, thetranslation of lenses 16 and 18 of output lens array 12 downward, in thedirection of arrow II, is accompanied by upward translation of inputlenses 36 and 38 of input lens array 32, in the direction of arrow I.The upward translation of diverging lenses 36 and 38 of FIG. 7 has asthe same effect as the downward translation of lenses 16 and 18 of FIG.6, in that the apertures of the lenses of the output lens array are notoverfilled.

When converging lens array 12 and collimating lens array 32 aretranslated by the amounts Δ₁ and Δ₂, respectively, the beam steer anglesθ_(x) as illustrated in FIG. 6b is given by the expression ##EQU1##where ##EQU2## and

f₁ and f₂ are the focal lengths of the lenses of arrays 12 and 32,respectively. By selecting the position of collimating output lens array32 such that

    Δ.sub.2 =(f.sub.2 /f.sub.1)Δ.sub.1 +Δ'.sub.1(3)

the steer angle is determined by the translation of the input converginglens array 12, and output collimating lens array 32 does not affect thesteer angle, so steering of the beam may be first accomplished bytranslation of input lens array 12, and when the input apertures of theoutput lens array are on the verge of overfilling, whereby vignettingmight begin to occur, the translation of input lens array 12 is stopped,and translation of output lens array 32 may be used for further beamscanning pursuant to equation (1).

The dual-translation scheme described in conjunction with FIGS. 6 and 7may be used in cascade or combination with the phase shifters describedin conjunction with FIG. 5. The combination provides the advantages overthe prior art of a wider range of continuous scanning without reductionof peak amplitude and generation of sidelobes.

FIG. 8a illustrates phase shifter array 540 including transparent phaseshifter elements or cells 546 and 548 cascaded with converging lenses 16and 18 of a first lens array 12 and lenses 234 and 236 of an output lensarray 32. In FIG. 8a, phase shifter array 540 is on the input side ofthe cascade, in FIG. 8b phase shifter array 540 lies between the lensarrays, and in FIG. 8c phase shifter array 540 is behind or on theoutput side of the cascade. In FIG. 8b, phase shifters 546 and 548 ofphase shifter array 540 are located at or near focus plane 99. In FIGS.8a, 8b and 8c, output lens array 32 is translated parallel to arrow Ifor deflection. As mentioned in conjunction with FIG. 5, the phaseshifter elements of phase shifter array 540 are controlled to correctfor piston phase error, to thereby achieve a continuous scan range.

FIG. 9 illustrates a cascade of a phase shifter array 540, a diverginglens array 32, and a converging lens array 12, with the phase shifterarray before, between and behind the lens arrays, respectively, and withoutput converging lens array 12 being translated for scanning. In FIG.9a, phase shifter 540 has its phase shifters 546 and 548 located betweenthe source array (not illustrated) and diverging lenses 36 and 38 ofdiverging lens array 32. Converging lenses 16 and 18 of converging lensarray 12 are translatable parallel to the direction of arrow I. In FIG.9b, phase shifter array 540 is located between the converging lens array32 and converging lens array 12, and in FIG. 9c phase shifter array 540is the last element of the cascade.

FIGS. 10a, 10b and 10c are similar to FIGS. 8a, 8b and 8c, respectively,with the exception that both lens pairs are translatable. In FIG. 10a,light beams 24 and 26 from the sources (not illustrated) passes throughphase shifter cells 546 and 548, respectively, of phase shifter array540, and then through the lenses of the cascade of lens arrays 12 and32. In FIG. 10b, the phase shifters of phase shifter array 540 arebetween the lens arrays at or near focal plane 99, and in FIG. 10c phaseshifter array 540 follows the output lens array 32.

FIGS. 11a, 11b and 11c are similar to FIGS. 9a, 9b and 9c, respectively,except that both lens arrays are translatable. In FIG. 11a, phaseshifters 546 and 548 of phase shifter array 540 receive light beams 24and 26 from an array of sources (not illustrated). Phase shifted lightfrom phase shifter array 540 passes through diverging lenses of lensarray 32, and then through the converging lenses of lens array 12. InFIG. 11b, phase shifter array 540 is between lens arrays 32 and 12, andin FIG. 11c phase shifter array 540 follows output lens array 12.

The arrangements of FIGS. 8, 9, 10 and 11 have the advantages of acontinuous range of scanning, with increased maximum beam amplitude atlarge scan angles, by comparison with the prior art arrangement.

FIGS. 12a and 12b illustrate a liquid crystal phase shifter cell whichmay be used in an array such as array 540 of FIG. 5a, and which isdescribed in the aforementioned Cassarly et al. paper. FIG. 12aillustrates a liquid crystal phase shifter cell including transparentglass side walls 1210 and 1212, transparent conductive coatings such asindium-tin oxide alloy coatings 1214 and 1216 applied to the innersurfaces of walls 1210 and 1212, respectively. A voltage sourceillustrated by a battery symbol 1218 is connected to conductor surfaces1214 and 1216 to apply a voltage to the highly birefringement nematicliquid crystals contained within the cell. Molecules of the liquidcrystal material are illustrated as small ellipses designated 1220. Asillustrated in FIG. 12a, representing a relatively low voltagecondition, the liquid crystal molecules are oriented with their axes ina particular direction, represented in FIG. 12a by a verticalorientation of the major axes of the ellipses. Light represented byarrows 1222 which passes through the cell is phase shifted by an amountwhich depends upon the rotation of the liquid crystal rotation.

FIG. 12b represents a situation in which a liquid crystal cell has ahigher applied voltage. As illustrated in FIG. 12b, at least some of themolecules are rotated, thereby affecting the index of refraction toimpart a phase shift different from that imparted in the conditionillustrated in FIG. 12a. As discussed in the paper, phase shifts ofgreater than 2π are possible, depending upon cell thickness.

FIG. 13 illustrates a prism phase shifter cell which may be arrayed withother like cells to produce a prism-like effect, by which light enteringat different locations along the cell can be phase shifted by differingamounts, thereby creating a tilted phase front at the output whichcauses the direction of propagation of light passing through the prismcell to be changed or scanned. In FIG. 13, elements corresponding tothose of FIG. 12 are designated by the same reference numerals. Asillustrated in FIG. 13, a first voltage source illustrated as 1224 isconnected between conductors 1214 and 1216 of the cell at the bottom ofthe cell, and another voltage source 1226, having a different voltage,is applied across conductors 1214 and 1216 at the top end of the cell.As a result of the voltage difference, current flows through thetransparent conductors 1214 and 1216, and a voltage gradient isestablished between conductors 1214 and 1216 within the cell, whichvoltage progressively increases between the bottom and the top cell. Thevoltage gradient results in progressively greater rotations of themolecules 1220 therein as a function of position within the cell. Inparticular, molecules 1228 at one end are rotated by a greater amountthan molecules such as 1230 at the other end. As a result of thedifference in rotation of the liquid crystal molecules along the lengthof the cell, the phase shift imparted to light traversing the cellvaries, so as to change the direction of propagation of the light asillustrated by the directions of arrows 1222 and 1232 in FIG. 13.

It should particularly be noted that a prism cell such as that of FIG.13 may impart both a constant phase shift component and a sloped orprism-type phase shift by appropriate application across the cell of aconstant voltage component and a voltage gradient component. Forexample, if source 1226 produces 1.2 volts and source 1224 produces 1.6volts, a constant 1.2 volts appears across the cell in conjunction witha voltage gradient of 0.4 volts. Thus, an array of prism cells canperform the functions of both piston phase shift and prism phase shift.

Prism phase shifter cells such as that of FIG. 13 may be arrayed in themanner illustrated in FIG. 5, and such an additional array may becascaded with an arrangement such as that of FIG. 5 or with one of thoseof FIGS. 8, 9, 10 or 11 to provide further deflection. When an array ofprism phase shifters such as that of FIG. 13 is arrayed with pairs ofconverging lenses such as with FIGS. 6, 7, 8 or 10, the array may haveless of a scanning range when the array of prism phase shifters isplaced directly on focus plane 99, because a substantial part of thelight would in that case pass through the center of each prism cell, andthe desired progressive phase shift arising from the passage of lightthrough different portions of the phase cell would not occur. A prismphase shifter array placed near the focus of a two-lens array system maybe used to aid in reducing overfilling of the apertures of the lenses ofthe output array. As mentioned, if phase shifter array 540 of FIGS. 5,8, 9, 10 or 11 includes prism cells as described in FIG. 13, only onephase shifter array is needed.

FIG. 14 illustrates a reflective phase shifter array. In FIG. 14, anelectrically conductive mounting block 1410 supports an array ofpiezoelectric actuator 1412a, 1412b . . . 1412n . . . 1412N. Eachpiezoelectric actuator 1412 supports an optically reflective surfaceillustrated as 1414a, 1414b . . . 1414N. Reflective surfaces 1414 havemutually parallel normals. The normal of reflective surface 1414n isillustrated as 1416. As is well known to those skilled in the art, lightrepresented by a dash line 1490a arriving at an undeflected reflectivesurface and making an angle θ₀ with normal 1416 is reflected (line1490b) at the same angle relative to the normal. Solid line 1492arepresents the incoming light ray, which reflects from deflectedreflector 1414n to reduce reflected ray 1492b. The change in opticalpath length is approximately d₁ +d₂ when θ₀ is small, and may becalculated as 2 d cos θ, where d is the amount of movement of thereflector surface. As illustrated in FIG. 14, a common electricalconductor 1418 is connected to mounting 1410, and is therefore connectedto all elements 1412. Each element 1412 is connected by a separateconductor to the control arrangement. The control conductor for element1412n is illustrated as 1420n. Voltage applied to conductor 1420nrelative to conductor 1418 causes motion of element 1412n.

The array illustrated in FIG. 14 may be used for providing piston phaseshifts in accordance with the invention. As illustrated in FIG. 15, asource array illustrated as 1522 produces beams of light illustrated as1524 which are directed at the reflective elements of array 1400. Thephase shifter array is oriented so as to reflect the light beams,suitably phase shifted under control (not illustrated) to a cascade oflens arrays such as 12 and 32, which may be relatively translated asdescribed in detail above. By bending the light path, a reflective phaseshifter array such as 1400 of FIG. 14 may be used between a pair of lensarrays, or following the output lens array.

FIG. 16 illustrates normalized irradiance as a function of scan angle ofthe main light beam in the far field of an arrangement such as that ofFIGS. 2 or 3 on a laboratory set up. As illustrated in FIG. 16,normalized irradiance is unity at near-in (0° to 2°), but the amplitudeof large angles, such as at 10°, falls to as low as 0.2. FIG. 17illustrates the normalized irradiance using an arrangement according tothe invention, such as that of FIGS. 6 or 7. As illustrated, theirradiance at 10° is greater than 0.4, corresponding to an increase inpower of about 3 dB. The improvement is believed to be less than thatachievable with a more sophisticated assembly.

FIG. 18a illustrates a first lens array 1812 and a second lens 1832, inwhich the lenses of the lens arrays have different diameters butidentical focal lengths, and nonperiodic or random element-to-elementspacing. When lens array 1832 is translated upward relative to lensarray 1812 as illustrated in FIG. 18b, same kind of scanning takes placeas would be the case if the lenses had periodic spacing. However, thefar-field sidelobes are substantially reduced by the effectiverandomization of the period of the array.

FIG. 19 illustrates a plan view of an arrangement according to theinvention, in which the arrays are curved. In FIG. 19 an array 998 oflaser diodes include diodes 998a, 998b . . . 998N, which direct theirlight beams radially away from a central point 996. Each laser may havedimensions which define an angle α subtended by the laser beam as seenfrom center 996. A curved array 994 of lenses includes lenses 994a, 994b. . . 994N, which are spaced in a corresponding manner, i.e. thephysical dimensions of the individual lenses are selected so that thelenses subtend the same angle α as seen from the center 996, wherebyeach lens is associated with one laser, and the lasers of array 998 areregistered with the lenses of array 994, so that the light beam from alaser passes through a corresponding lens, even though the lateraldimensions of the array elements differ.

From the above discussion of FIG. 19, it will be clear that the angularspacing of the elemental lenses 992a, 992b . . . 992N of a curved secondlens array 992 is also α, and that the lenses of array 992 areregistered with the lenses of array 994 and lasers of array 998 eventhough the lateral dimensions differ. Arrays 992 and 994 may betranslated in a direction in and out of the plane of the FIGURE, assuggested by the x (into the FIGURE) adjacent array 994 and the . (outof the FIGURE) adjacent array 992. If a phase-shifter array is used, assuggested by dotted-line outline 990, the same dimensioning is used.

While straight-line translation into and out of the plane of FIG. 19 maybe used as described above, a relative rotational movement of the arraysabout a center point 996 will also provide beam scanning. Thus, array998 as illustrated in FIG. 19 may be considered to be a sectional viewof a two-dimensional array curved into a spherical form.

Other embodiments of the invention will be apparent to those skilled inthe art. For example, array of sources 522 of FIG. 5 may be translatedrelative to microlens array 510 instead of translating the microlensarray. The various arrays have been illustrated with relatively smallnumbers of elements, but arrays of hundreds, thousands or even moreelements may be useful. Arrays of laser diodes have been described asthe source, but other sources of light or electromagnetic radiation maybe used, and the same principles may be used for microwaves ormillimeter-waves or for other electromagnetic radiation having longer orshorter wavelengths than light, so long as the lenses and phase shiftersare appropriately dimensioned. While the lenses of the arrays have notbeen described in detail, they may be round or oblong to match thecross-sectional shape of the associated light beams, and their curvaturemay be continuous, or it may be binary as known in the art.

What is claimed is:
 1. A beam steering arrangement for a plurality ofsources of beams of electromagnetic radiation arrayed with a preselectedsource-to-source spacing, comprising:a first lens array, said first lensarray including a first plurality of lenses, said lenses of said firstlens array being arrayed with a lens-to-lens spacing which correspondsto said preselected source-to-source spacing, the lenses of said firstlens array being selected to be one of converging and diverging lenses,for generating output beams from the lenses of said first lens array,which output beams include diverging beam portions; a second lens array,said second lens array including a plurality of lenses, which pluralitymay equal said first plurality, said lenses of said second lens arraybeing converging lenses, for, when illuminated by diverging beams,collimating said diverging beams to produce collimated output beams;first mounting means coupled to said first lens array for holding saidfirst lens array to intercept said beams from said sources, for therebygenerating said diverging beam portions from said first lens array;second mounting means coupled to said second lens array for holding saidsecond lens array to intercept said diverging beam portions for therebygenerating said collimated output beams from said second lens array;first translating means coupled to said second mounting means and saidsecond lens array for translating said second lens array in a directiongenerally transverse to said beams, for thereby scanning said collimatedbeams, whereby scanning at some angles causes each of said divergingbeams to illuminate at least two adjacent ones of said output lenses,thereby resulting in reduction in peak amplitude of said collimatedbeams; and second translating means coupled to said first mounting meansfor translating said first mounting means and said first lens array in adirection generally parallel to said transverse direction, for scanningsaid output beams of said first lens array so that each of said outputbeams of said first lens array substantially illuminates only one ofsaid lenses of said second lens array.
 2. An arrangement according toclaim 1 wherein said lenses of said second array are converging lenses.3. An arrangement according to claim 2 wherein said first translatingmeans translates said second mounting means in a direction correspondingto the desired direction of deflection of said collimated beams.
 4. Anarrangement according to claim 3, wherein said lenses of said first lensarray are diverging lenses, and said second translating means translatessaid first mounting means in a direction opposite to that of the desireddirection of deflection of said collimated beams.
 5. An arrangementaccording to claim 3 wherein said lenses of said first lens array areconverging lenses, and said second translating means translates saidfirst mounting means in a direction corresponding to the desireddirection of deflection of said collimated beams.
 6. An arrangementaccording to claim 1 wherein said lenses of said first lens array aredimensioned to be larger than the cross-sections of said beams from saidsources, so that the input apertures of said lenses of said first lensarray are underfilled.
 7. An arrangement according to claim 1 whereinsaid lenses are binary.
 8. An arrangement according to claim 1 whereinsaid preselected source-to-source spacing is more than one wavelength ata frequency near that of the frequency of maximum amplitude radiation.9. An arrangement according to claim 1 wherein said sources are arrayedin line.
 10. An arrangement according to claim 1 wherein said sourcesare arrayed in two dimensions.
 11. An arrangement according to claim 1wherein said lens arrays have regular spacing between elements.
 12. Anarrangement according to claim 1, further comprising an array of aplurality of phase shifters, which plurality may equal said firstplurality;mounting means coupled to said array of phase shifters formounting said phase shifters in cascade with said first and second lensarrays; and control means coupled to said array of phase shifters forcontrolling said phase shifters for phase-shifting said beams in saidcascade so as to reduce toward zero the phase difference betweenmutually adjacent beams for reducing grating lobe effects.
 13. Anarrangement according to claim 12 wherein said phase shifters of saidarray of phase shifters are liquid crystal phase shifters.
 14. Anarrangement according to claim 12 wherein said phase shifters of saidphase shifter array are reflective.
 15. A beam steering arrangementcomprising:a plurality of sources of beams of electromagnetic radiationarrayed along curves centered on a point and with preselectedsource-to-source spacing: a first lens array, said first lens arrayincluding a first plurality of lenses, said lenses of said first lensarray being arrayed with a lens-to-lens spacing which corresponds tosaid preselected source-to-source spacing, the lenses of said first lensarray being selected to be one of converging and diverging lenses, forgenerating output beams from the lenses of said first lens array, whichoutput beams include diverging beam portions; a second lens array, saidsecond lens array including a plurality of lenses, which plurality mayequal to said first plurality, said lenses of said second lens arraybeing converging lenses, for, when illuminated by diverging beams,collimating said diverging beams to produce collimated output beams;first mounting means coupled to said first lens array for holding saidfirst lens array to intercept said beams from said sources, for therebygenerating said diverging beam portions from said first lens array;second mounting means coupled to said second lens array for holding saidsecond lens array to intercept said diverging beam portions for therebygenerating said collimated output beams from said second lens array;first translating means coupled to said second mounting means and saidsecond lens array for translating said second lens array in a directiongenerally transverse to said beams, for thereby scanning said collimatedbeams, whereby scanning at some angles causes each of said divergingbeams to illuminate at least two adjacent ones of said output lenses,thereby resulting in reduction in peak amplitude of said collimatedbeams; and second translating means coupled to said first mounting meansfor translating said first mounting means and said first lens array in adirection generally parallel to said transverse direction, for scanningsaid output beams of said first lens array so that each of said outputbeams of said first lens array substantially illuminates only one ofsaid lenses of said second lens array.
 16. A method for steering aplurality of beams from an array of sources of beams, comprising thesteps of:passing each of said beams from one of said sources through alens of a first lens array selected for forming a beam including adiverging beam portion; intercepting each of said diverging beamportions with the input aperture of a converging lens of a second lensarray for forming a plurality of collimated beams; translating saidsecond lens array in a direction transverse to the undeflected directionof propagation of said collimated beams to deflect said collimated beamsin a selected direction, whereby increased translation may result inoverfilling said input apertures of said lenses of said second lensarray, thereby reducing beam intensity; and translating said first lensarray in a direction generally parallel to said direction of translationof said second lens array in a manner selected to reduce saidoverfilling of said input apertures of said lenses of said second lensarray and thereby restore said beam intensity.
 17. A method according toclaim 16 further comprising the step of phase-shifting at least one ofsaid beams from said array of sources, said beams including divergingbeam portions, and said collimated beams for reducing toward zero thephase difference between adjacent portions of adjacent ones of saidcollimated beams.